Implement performance and race condition tests for terminal session service

[mattheworiordan]

Several tests in terminal-session.service.test.ts are currently skipped:

1. "should handle concurrent session operations" - Needs proper implementation for testing race conditions
2. "should clean up sessions on server shutdown" - Needs implementation for testing graceful shutdown
3. "should enforce session limits per user" - Needs implementation for testing session limiting logic

These tests are important for ensuring the terminal session service handles concurrent operations and resource limits correctly.